St. Paul daily globe. [volume] (Saint Paul, Minn.) 1884-1896, 1887-03-01
UNDER THE RIVER BED.
The Perilous Trip Into the Air Chamber
Of the Great Steel-Arch
Oaisson.
How Men Work Under the Heavy Air
Pressure of Often Two At
mospheres.
Lowering the Gigantic Structure OF
Masonry and Timber Below
the River Bed.
Globe Reporter Makes the Trip
and Tells Something of What
He Saw There.


hanger. Thousands of foolish risks daily
incurred bear out this statement Supt.
Thomas Barber. who has charge OF the
work of sinking the great caisSOn of the
steel arch bridge, is impressed with its truth
every day, from the number of applications
made to be allowed to descend to the air
chamber of the caisson, and which he Of
course refuses. Since the great caisson at
St. Louis was overwhelmed and two scores
Of lives sacrificed, the general public is pretty
well informed of the danger of working be-
meath the bed of the river under pressure
Of two atmoSphereS and beneath a mon
strouS pile of masonry. This knowledge
Induces a great crowd TO stand constantly
sn the suspension bridge and gaze curouSly
when, at the shifting of the gangs. line of
hen crawl out of the air trap and show up
ike rats from a sewer.
IN take you down in the interest of the
public and at your own risk" said Supt.
Barber, when GLOBE reporter made APP
plicatiOn to descend to the subterranean and
iub-aQuan vault beneath; and So clutching
In accident policy, the reporter went down
An obliging workman rendered the uSe,of a
rubber suit with the remark: ''Begorrah,
Sut thin dude clothes would suffer, me
Doy."
THE CAISSON.
Is is we'll known, is simply an inverted box,
iorced to the bed of the river with many
ions of masonry piled upon it to hold it
Iown. This box is ia feet long, 20 feet
kide and seven feet deep, constructed OF
three layers OF 12X12 timberS. The edges
ef the box. which rest on the bed of the
FLYER, are beveled down to cutting edge
Ind heavily Shod with iron. After the box
MAS lowered 10y jacks until supported by its
Swn buOyancy and that of the inclOsed air,
he masonry of the pier was begun and the
Box thus weighted down until it rested in
he silt of the river bed. Then began the
work of sinking, as the entire caisson must
10 below the bed, hard and fast into
HE Sandrock. To sink it, it is necessary
% remove the sand from beneath the
.aisson and permit it gradually to descend
until the required depth is reached. The
trst process is to force compressed air into
The box sufficient to overcome the pressure
if the water. For that purpose an engine
S located on the bank of the river and a
iOubIe force pump sends the air into the
!hamber. The sand and rock are then re-
hoyed from the inside and the immense
Weight sinks gradually to the desired spot.
UNDER THE IMMENSE PRESSURE
kantly at work, three gangs, relieving
ZACH other alternately and working eight
tours at stretch. AS fast as the sand is
hoveled up it is conveyed out through pipes
ind thrown upon the ice, the caiSsOn sinking
neadily. Meanwhile the work of building
he pier continues without interruption.
iver one thousand tons of masonry having
Hready been laid, in six courses.
This was the situation when the GLOBE
eporter donned his borrowed uniform and
beloved the superintendent up the ladder
the top OF the air lock leading to the bowels
If the structure. This lock is a large tube
If heavy boiler iron, six feet in diameter at
he top, and, after eight feet, diminishing
b diameter Of three feet The tube runs
rom the bottom of the caisSon and projects
hove the masonry Oh top. TO prevent the
scape of the compressed air within the
nbe is trapped, or Waived. above and below,
allow the coming and going of the work.
hen, the valves consisting of huge plates
cast iron. shutting upon heavy washers
rubber and operating by means of block
md tackle.
Z BENEATH THE RIVER BED.
climbing down the tube by means of iron
land-holds, the little party stood within the
Dck and received instructions. The
md when all was ready the
daylight and air were excluded by the
ieavy door above, few sckly candles
living dim illumination that made the
enderfeet feel decidedly shaky, When the
Upper trap was secure, the leader turned
lalye and, with fierce Kissing noise, the
Imprisoned air below rushed in and filled
he little chamber. The pressure was
bout i've pounds to the square inch and
liter the first sensation of rupturing the
ar drums was over, was nc longer notice.
Dle. The lower trap was opened, and by
Aeans Of the iron ladder the party passed
Rpidly down the thirty feet of descent and
TODD upon the sand-beneath the masonry.
he heavy timber. the clust of the river,
md below the bed of the stream itself. 4
ozen Workmen were busily engaged in
hoveling the sand into heaps beneath the
ION pipe which is to convey it to the upper
IL, each of these pipes being closed at the
bttom by valve ..
BLOWING HER OUT"
The pressure is now comparatively
ight, said Supt. Barber. Until we get
leeper she wont stand much. We are forcing
Tout beneath the cutting edges now. But
Is wonderful what this pressure amounts
D. Don't get frightened now, but observe. :"
ioing to one of the pipes mentioned he
pened the valve; there was terrific rush of
he imprisoned air accompanied by Wheel
ne and grooming OF the entire structure as
aused the reporter to clutch timber and
walt IN desperation the fate that seemed
imminent. The hugh caiSSon trembled and
eSan sinking the sharp edges cutting their
FAY through the sand until the structure
lad sunk six inches. At the same time
ne pumps had been stopped. and the water
egan slowly to creep in. 1t was ali i'm
nense relief when the valve was closed.
nd the monotonous clang of the pumps re-
Dmmenced. 1t seemed incredible that the
Drce OF the compressed air would sustain
ne gigantic weight put upon it; yet it must
X remembered that with only pressure OF
TX pounds 10 the square foot the force of
he air amounted to about 1000 tons. In
NO weeks this pressure will be quadrupled!
THROWING OUT THE SAND
accomplished by atmospheric pressure.
The sand is piled in heaps about each of
he iron pipes mentioned above and the
ave opened. The pressure of the all
Pthin the caisSon forces it out in a shower.
he men Keeping the sand filled in to the
asst. When the sand rock is reached and
he pressure increased it will be forced ont
the same way. Concrete will then be
ent down and the air chamber filled hard
nd solid, which completes the caisson
FORK.
Under a pressure of as high as thirty
pounds to the square inch. or two atmos-
Meres, most men can work reasonably
YelI They have been known to work
mder pressure of three atmospheres.
ut such work brings OH what is called
bead" disease of tue marrow, likened
INTO most excruciating rheumatism.
After stay of nearly an hour beneath